ARM: sun6i: Relicense the A31 DTSI under GPLv2/X11

The current GPL only licensing on the DTSI makes it very impractical for other
software components licensed under another license.

In order to make it easier for them to reuse our device trees, relicense our
DTSI first under a GPL/X11 dual-license. Hopefully, the DTS will follow soon.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Carlo Caione <carlo@caione.org>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>